The substrate on which the integrated circuit is produced may be a silicon-on-insulator (SOI) substrate and more particularly a fully depleted silicon-on-insulator (FDSOI) substrate, without these examples being limiting.
A silicon-on-insulator substrate comprises a semiconductor film, for example made of silicon or a silicon alloy, for example a silicon-germanium alloy, located on top of a buried insulating layer, commonly called a “BOX” (for “buried-oxide”), itself located on top of a carrier substrate, for example a semiconductor well.
In FDSOI technology, the semiconductor film is fully depleted, i.e. it is composed of intrinsic semiconductor material. It is generally about a few nanometers in thickness. Moreover, the buried insulating layer is itself generally thin, of about ten nanometers in thickness.
On account of the small thickness of the semiconductor film, the source and drain regions of transistors comprise segments that are raised relative to the semiconductor film, so as to ensure an adequate electrical connection between these regions and the channel region of the transistor.
Such raised source and drain regions (RSDs) are typically obtained by epitaxy.
In order to allow the raised source and drain zones to be produced by epitaxy, the surface of the silicon is cleaned beforehand, for example using a deoxidation process, this causing cavities to form in the neighboring insulating zone.
Moreover, in commonplace integration processes, when it is desired to produce a contact on an active zone located a small precisely controlled distance from a polysilicon line, for example located between two polysilicon lines, the use of a photolithography mask to define the geometry of the contact then leads to the production of a contact that projects over said insulating cavity.
Furthermore, in this case, the conventional production process of the contact leads to the cavity being pierced, then causing a short-circuit between the metal end of the contact and the neighboring portion of the carrier substrate.
One way of avoiding this piercing consists in using two photolithography masks to define the geometry of the contact so that the latter does not project from the active zone.
However, such a process is expensive to implement.